This invention relates to bonding resins and particularly to the use of renewable resources in or as substitutes for formaldehyde-based resins.
The wood products industry is still almost entirely dependent on chemicals derived from petroleum and natural gas for producing the necessary bonding agents. The application of bonding agents enables the use of smaller trees, wood chips, fibers and mill residues to produce various products that meet the consumer needs. As the quality of harvested timber declines due to the shrinking commercial forest land base, the future of wood utilization will require an even higher dependence on bonding agents to convert the limited timber resources into needed products. In view of the environmental strains caused by fossil fuels and chemicals and their inherent vulnerable and limited supply, the efforts to identify other available resources for bonding raw materials have accelerated in the latest decades. Renewable resources are he most promising in this field and much research and development have been devoted in this area.
Formaldehyde-based resins (urea-formaldehyde (UF), phenol-formaldehyde (PF), melanine-formaldehyde (MF), melamine-urea-formaldehyde (MUF), resorcinol-formaldehyde (RF), tannin-formaldehyde (TF) and mixtures thereof) are most commonly applied in composite wood panel manufacture. The components of these resins are mainly derived from oil and/or natural gas. It is the aim of the present application to provide effective resin substitutes derived from natural products such as renewable forest biomass and agricultural residues.
Numerous studies were based on the role of products of natural origin in providing alternative feedstocks for wood adhesives. Chen, C. M., xe2x80x9cGluability of Copolymer Resins Having Higher Replacement of Phenol by Southern Pine Foliage Extracts for Flakeboards and Composite Panelsxe2x80x9d, Holzforschung, 1993, 47 (1), 72-75, xe2x80x9cState of the Art Report: Adhesives from Renewable Resourcesxe2x80x9d, Holzforschung und Holzverwertung, 1996, 4, 58-60, xe2x80x9cA Hulluva Switch: Inventor Finds Value in Peanut Hullsxe2x80x9d, The University of Georgia, Research Reporter, 12-13, reported that extracts of peanut hulls, pecan nut pith or pine bark and foliage can be used to replace up to 80% of the phenol used for phenol-formaldehyde resins. The extraction process involved several stages and was time-consuming.
Efforts have been made also to utilize the oil obtained by the pyrolysis of biomass or its phenolic fraction to substitute phenol in the production of phenol-formaldehyde resins, Gallivan, R. M., Matschei, P. K., xe2x80x9cFractionation of Oil obtained by Pyrolysis of Lignocellulosic Materials to recover a Phenolic Fraction for use in making Phenol-Formaldehyde Resinsxe2x80x9d, U.S. Pat. No. 4,209,647, 1980; Diebold, J., Power, A., xe2x80x9cEngineering Aspects of the cortex Pyrolysis Reactor to Produce Primary Pyrolysis Oil Vapors or Use in Resins and Adhesivesxe2x80x9d, Research in Thermochemical Biomass conversion, Bridgwater, A. V., Kuester, J. L., Elsevier Applied Science, London, 1988, 609-628; Chum, H. L., Diebold, J. P., Scahill, J. W., Johnson, D. K., Black, S., Schroeder, H. A., Kreibich, R. E., xe2x80x9cBiomass Pyrolysis Oil Feedstocks for Phenolic Adhesivesxe2x80x9d, Adhesives from Renewable Resources, R. Hemingway and A. Conner, Eds., ACS Symp. Series, No. 385, 1989, 135-151; Chum, H. L., Black, S. K., xe2x80x9cProcess for Fractionating Fast-Pyrolysis Oils, and Products derived therefromxe2x80x9d, U.S. Pat. No. 4,942,269, 1990; Chum, H. L., et alk. xe2x80x9cInexpensive Phenol Replacements from Biomassxe2x80x9d, Energy from Biomass and Wastes XV, Eds. Klass, D. L., 1991, 531-540. Substitution levels of up to 75% have been reported, however the low amount of phenolic compounds present in the oil necessitates a factionation step, which raises the final product cost.
The spent liquor obtained from the paper manufacturing process, comprising mainly the degradation products of lignin, has been the subject of a large number of studies relating to its applicability in formaldehyde-based adhesive systems (mainly PF-adhesives), Forss, K. J., Fuhrmann, A., xe2x80x9cFinnish Plywood, Particleboard, And Fibreboard Made With a Lignin-Base Adhesivexe2x80x9d, Forest Prod. J., 1979, 29 (7), 36-43; Doering, G. A., Harbor, G., xe2x80x9cLignin Modified Phenol-Formaldehyde Resinsxe2x80x9d, U.S. Pat. No. 5,202,403; Chen, C. M., xe2x80x9cGluability of raft Lignin Copolymer Resins on Bonding Southern Pine Plywoodxe2x80x9d, Holzforschung, 1995, 49 (2), 153-157; Senyo, W. C., Creamer, A. W., Wu, C. F., Lora, J. H., xe2x80x9cThe Use of Organosolv Lignin to Reduce Press Vent Formaldehyde Emissions in the Manufacture of Wood Compositesxe2x80x9d, Forest Prod. J., 1996, 46 (6), 73-77. Various replacement scenarios have been tested, yet the low reactivity of this Liquor cannot justify its use without including any additional modification steps.
In the use of these materials single products have been employed and attempts to improve performance have been made by modification of the material usually to try and increase the phenolic content.
According to the present invention there is provided a phenol/aldehyde resin system in which a significant proportion of the phenol component conventionally employed in such resin is replaced by a mixture of at least two different natural phenolic materials.
The invention also provides a method of forming composite materials in which a proportion of the phenol/aldehyde resin component is replaced by a phenol/aldehyde resin system of the invention.
An advantage of the invention is that it permits lowering of resin toxicity by use of the natural substitutes now specified instead of toxic petroleum derived phenolic products. Thus the phenol/aldehyde resin system of the invention provides an advantage in that it enables replacement of conventional phenol materials even though the properties of the resin system are not superior to those achieved by normal phenol materials.
The phenol/aldehyde resin systems which can be modified in accordance with this invention are those which are conventional in the manufacture of bonding agents and adhesives. The term xe2x80x9cbonding agentxe2x80x9d is used generically to include adhesive materials. The most common of these resins is, of course, phenol/formaldehyde but phenol can be replaced by other materials within the generic term phenol for example cresol or resorcinol to the extent that this is conventional in the phenol/aldehyde resin art and formaldehyde can be replaced by certain other aldehydes although this is not so common In the art. Those skilled in the art of using phenol/aldehyde resins will be well aware of the alternatives and combinations available. The choice of phenois and aldehydes will normally be related to the types of resins employed for the bonding of composite products but he invention is also applicable to phenol/aldehyde resins employed in other bonding and adhesive functions.
Each of the natural phenolic materials which are used in part substitution of the phenol component of the conventional phenol/aldehyde resin will be derived from a natural source. The difference between these materials can arise from the nature of the source or from a variation in treatment of the same natural source so as to provide materials with different properties for example the nature of the phenolic compounds or their proportion. Each of the materials will have, however, a significant content of phenolic components. The phenolic content can be free phenols or phenolic groupings in molecules forming part of the material. By phenolic content is meant the presence in the molecular structure of one or more components (eg. polymeric components) of phenol structures, i.e. hydroxy substituted aromatic groupings or molecular groupings exhibiting the characteristic properties of phenols. Phenol may be present but usually the component is a compound with a phenolic grouping. Since the natural materials employed in forming the combinations of the invention are often derived from lignin, a natural polymer containing phenolic groups in the structure, extracts, or modifications of such materials will contain phenolic content. The material can be a natural plant derived material or by-product of processing a natural material. The phenolic content can be the normal content or an enhanced content. Enhancement of the phenolic content can be achieved by various treatments of natural materials, particularly lignins for example extraction or pyrolysis.
Thus each component of the system can be a biomass pyrolysis oil or a spent liquor obtained from a paper manufacturing process or other manufacturing process applied to natural materials which contain phenolic containing components. Thus there could be used extraction products of forest biomass or agricultural residues including tropical species residues.
Although thee invention is directed to at least two different natural phenolic materials there could be more than two materials, each material could comprise a mixture of two or more materials. One very suitable component would be a natural product which contains a significant and large proportion of phenolic material for example certain nut shell oils particularly cashew nut shell liquid. A number of natural product materials and by-products are known which contain significant contents of phenolic components. As mentioned above these can be for example lignins.
It is surprising to find that, by combining at least two different natural materials containing a proportion of phenolic components the resulting combination demonstrates a synergistic effect and enables substitution levels of up to 80% of the phenolic component of a standard formaldehyde-based resin. From another point of view, therefore, the invention lies in the combination of at least two different natural materials, both of which contain phenolic compounds as a substitute for the phenolic component of a phenol/aldehyde resin. It is surprising to find that the simple combination of phenolic materials gave an improvement more than would have been expected by the mere increase in he content of phenolic components. It is surprising to find that combination of natural phenolic materials gives en improvement which is more than would have been expected by the change, particularly any increase in the content of phenolic component.
The different Phenolic components can be simply blended when it is desired to employ them or can be subjected to conditions which cause interaction between the components.
The substitute composition can be used in the synthesis of the resins for bonding the final composite material or can be used in the actual production of composite panel products. Although the invention relates primarily to the formation of composite materials using bonding agents prepared with such combinations, improvements have been found for other bonding or adhesive systems employing formaldehyde-based resins especially phenol-formaldehyde resins.
The compositions of the invention can be used in combination with other natural materials such as tannin to obtain a totally natural resin product.
The amount of the phenolic content materials employed can be determined by adding increasing amounts of one phenolic material to a different material to the point at which a distinct improvement in the bonding properties or adhesiveness is noted, particularly in a cured final composite material. Increasing the content of one phenolic material beyond a certain proportion is not advantageous since the bonding or adhesiveness obtained will not significantly be advantageous over use of normal phenolic materials used in such resins. In other words, the amount of each phenolic material added is determined by the increase in synergistic effect as compared to simply adding one phenolic material to resins. The amounts added can therefore be readily determined by one skilled in the art. Thus adding one material may allow substitution of phenol up to a certain percentage by weight and beyond that a deterioration of the composite product properties is observed. It is surprising to find that the combination of several natural derivatives of phenolic character can allow up to 80% phenol substitution without impairment of the composite properties.
The formaldehyde and/or natural resins of the present invention can be applied in the manufacture of composite panel products such as particleboard, fibreboard [medium density fibreboard (MDF), high density fibreboard (HDF)], oriented strand board (OSB) and plywood.
It is also the subject of the invention to use combinations of the disclosed substitutes with formaldehyde and/or natural resins such as tannin resins and other binders such as polymeric diphenyl-methane diisocyanate (PMDI).